1. Field of the Invention
The present invention relates generally to a method for forming a capacitor of a semiconductor device, and more particularly to a method for forming a capacitor of a semiconductor device, in which an excellent leakage current characteristic as well as desired charging capacity can be ensured.
2. Description of the Prior Art
Recently, cells of a DRAM device has occupied a smaller area with increase in a degree of integration of the DRAM device, so it becomes more and more difficult to ensure charging capacity required. As is well known in the art, the charging capacity of a capacitor is proportional to an area of an electrode and a dielectric constant of a dielectric film, and is inversely proportional to a distance between electrodes, that is, a thickness of the dielectric film. For ensuring charging capacity required, therefore, it is necessary to reduce the thickness of the dielectric film or to apply materials having a large dielectric constant as the dielectric film.
Thereupon, in order to ensure charging capacity required, researches are being vigorously pursued to replace the existing Oxide-Nitride-Oxide (ONO) dielectric film by a single dielectric film of Al2O3 (ε=9), a single dielectric film of HfO2 (ε=25) or a dual dielectric film of HfO2/Al2O3 in which Al2O3 and HfO2 are simply laminated.
In terms of an unit process cost, it may be profitable to employ the single dielectric film of Al2O3 or Hfo2, but Al2O3 has a restriction on ensuring charging capacity because its dielectric constant is not so different from that of the existing Si3N4 material (ε=7), and HfO2 is thermally unstable and thus has a poor leakage current characteristic due to its low crystallization temperature although it has a large dielectric constant. As a result of this, it is practically difficult to solely apply Al2O3 or HfO2 as a dielectric film.
In order to solve the problem related to HfO2, a laminated structure of HfO2/Al2O3, in which Al2O3 and HfO2 are simply laminated, has been introduced. However, the simple laminated structure of HfO2/Al2O3 causes loss in charging capacity due to a low dielectric constant of Al2O3 and has a poor thermal stability at a high temperature because HfO2 is still easy to be crystallized. That is, the laminated structure of HfO2/Al2O3 has a problem in that its leakage current characteristic is deteriorated at a high temperature.
In addition, an HfxAlyOz thin film consisting of a solid solution of Hf and Al has been proposed recently. However, when the HfxAlyOz thin film is deposited at a temperature of 300° C. or less by an Atomic Layer Deposition (hereinafter referred to as ‘ALD’) technique using Tri-Methyl-Aluminum (Al(CH3)3; TMA) as a source of Al and Tetrakis(ethylmethylamino)hafnium (Hf[N(CH3)C2H5]4; TEMAH), impurities existing within the film, such as C and H, incur a technical problem of deterioration in a leakage current characteristic. Of course, an attempt may be made to improve electrical characteristics by subsequently performing heat treatment under a high reactive oxygen atmosphere after the formation of the HfxAlyOz dielectric film. In spite of such an attempt, however, it has been reported that an oxidation reaction is generated at an interface between the HfxAlyOz dielectric film and a storage electrode to cause deterioration in electrical characteristics.